1. Field of the Invention
This invention relates to an ink jet recording apparatus, more particularly to a tube pump construction which maintains or recovers the normal droplet discharge state of an ink jet head.
2. Related Background Art
In ink jet recording apparatuses of the prior art, for the purpose of a maintaining normal droplet discharge state of the ink jet head or recovering the normal discharge state when clogging occurs at the discharge port, there has been employed means for arranging a pump for recovery and suction of ink from the discharge port by the negative pressure of the pump. Also as the pump for recovery, there has been employed a tube pump which generates negative pressure by utilization of volume change within the tube. Such a tube pump has the merits of being simple and small in scale, and also such a pump can be formed at low cost.
The tube pump of the prior art, which performs continuous suction while squeezing an extended tube by a pressurizing roller, can increase the suction amount per unit time with difficulty. For, if the cross-sectional area of the tube is attempted to be increased, enlargement of the tube or enlargement of the pressurizing roller is brought about, whereby not only the cost is increased, but also the increase of cross-sectional area is limited.
In the tube pump mechanism of the prior art example used for recording head, during formation of the negative pressure, namely when the pressure changes from zero to maximum pressure, the constitution is constantly communicated to the head side. For this reason, when a discharge port where clogging is generated by dust clogging or bubbles at the discharge port and a normal, unobstructed discharge port exist, ink may be discharged from the normal discharge port considerably before the pump achieves the maximum pressure. In this case, when the pressurizing roller for tube pressurization reaches a point when maximum pressure can be generated, since the negative pressure accompanied with movement of the roller performs suction continuously therebefore, there has been loss of the negative pressure energy by ink flowout from the normal discharge port. Hence, the negative pressure applied to the discharge port where clogging has created the need for recovery is reduced. Accordingly, it may be also conceivable to increase the acting area of the tube or the pressurizing roller for further enhancing the maximum pressure, but it will bring about enlargement of the tube pump mechanism to bring about increased cost. Also, the waste ink created by this suction recovery is increased, whereby there has been involved the problem of lowering in running cost of the ink jet head. Also, in recovery of non-discharging which occurs by generation of bubbles inside of the ink jet head, while rapid flowout rate of ink during suction is more advantageous for bubble removal, in the tube pump mechanism of the prior art, because the constitution can not give momentarily maximum pressure, the flowout rate of ink is lowered, causing the drawback that efficiency of bubble removal is lowered.